Tuesday, October 16, 2012

At first, I
didn't notice the unusual antlers on this young white-tailed deer (Odocoileus
virginianus). His antlers were small, slightly deformed and
still covered with velvet in mid-September, the time of year when most of our
bucks are ready to rumble with hardened and polished antlers. His left side
looked to be growing a late but otherwise normal spike. The right side was
trying to grow a short, double main beam.

What might cause this odd antler
growth? Age and
genetics both play a roll in antler growth, but the primary factor is
nutrition. Antler deformities, however, are almost always caused by injury.

"Buck rub" tree

White-tailed
bucks grow their first set of antlers during their second summer. Antlers begin
growing inMarch or April and normally
finish by August or early September. First-year antlers are usually single
spikes that represent about 10% of his adult antler potential. A buck reaches 50%
of his antler potential at age three. And if he lives to maturity, at 5-8
years, he will fulfill his antler size potential only if his home range grows the
right kinds of foods in the right seasons.

While growing,
velvet-covered antlers are very delicate and easily damaged. Bucks will
carefully turn and twist their heads to avoid scraping their soft antlers
against branches. If roused to defense, he will use his sharpened hooves
instead of his antlers. It's injuries to velvety antlers that cause the sort of
irregularities that I eventually noticed on this young buck. Odd points, double main
beam, slow growth. Most injuries won't affect next year's antlers,
unless the injury occurs close to the antler base (the "pedicle") or on the
skull.

Asymmetrical white-tailed deer antlers

Full-grown
antlers harden in the fall, when bucks scrape off the velvet and polish their
new antlers brown by rubbing them against small trees, called
"scrapes" or "buck rubs." The bucks begin sparring and
establish a dominance hierarchy for breeding. Dominant males don't defend a
territory, but instead they defend the area around a doe and attempt to drive
away all competitors. After the breeding season, the bucks will start shedding
their antlers in February, later in more southerly states.

White-tailed
deer are primarily browsers (small stems and twigs, forbs), and they eat grass only in the spring. Springtime is the nutritional peak each year, and stems and forbs are
eaten in equal amounts. Selection for small stems and twigs slowly increases as
forbs decline in nutritional value through the summer. One shrub species,
Western Snowberry (Symphoricarpos occidentalis), accounted
for almost one-third of the summer contents of deer rumens sampled in the
Missouri River bottom lands of northcentral Montana.

In the fall, the end
of antler growth allows for fat build up. Deer will seek out foods with high levels of
carbohydrates, to be stored as fat reserves and used for fall breeding and winter
survival. Their winter diet is almost entirely woody browse.

All of this plant material must be broken down in the deer's four-chambered stomach. In the first chamber, the rumen, there are large quantities of bacteria and protozoa for just this purpose. What's interesting is that these microflora in the rumen are plant-specific. That is, one species of protozoa only works to break down one species of plant.

Spotting a healthy buck with large antlers is a favorite fall pastime in our neck of the woods. Spying one with atypical antlers is even more intriguing. Still, there's a lot more going on with these deer than what is visible to our eyes.